I=2 Two-Pion Wave Function and Scattering Phase Shift

TL;DR

This study calculates the I=2 two-pion wave function to analyze scattering phase shifts and interaction ranges, confirming the validity of finite size formulas and demonstrating improved statistical accuracy over traditional methods.

Contribution

It provides the first lattice calculation of the two-pion wave function for the I=2 channel, validating finite size formulas and showing advantages in phase shift extraction methods.

Findings

Interaction range is consistent across different quark masses.

Finite size condition is satisfied for the studied parameters.

Wave function method yields smaller statistical errors for phase shifts.

Abstract

We calculate a two-pion wave function for the I=2 $S$-wave two-pion system with a finite scattering momentum and estimate the interaction range between two pions, which allows us to examine the validity of a necessary condition for the finite size formula presented by Rummukainen and Gottlieb. We work in the quenched approximation employing the plaquette gauge action for gluons and the improved Wilson action for quarks at $1/a=1.63 {\rm GeV}$ on $32^3\times 120$ lattice. The quark masses are chosen to give $m_\pi = 0.420$, 0.488 and $0.587 {\rm GeV}$. We find that the energy dependence of the interaction range is small and the necessary condition is satisfied for our range of the quark mass and the scattering momentum, $k \le 0.16 {\rm GeV}$. We also find that the scattering phase shift can be obtained with a smaller statistical error from the two-pion wave function than from the two-pion time correlator.